A fuel control system of this type is typically adapted to asynchronously inject fuel in an amount greater than that ordinarily required during acceleration, thereby preventing a fuel mixture from becoming temporarily lean, due to a slow detection of intake air by an air-flow meter upon acceleration. In an attempt at preventing the fuel mixture from being difficult to gasify or vaporize before the engine has warmed up and, accordingly, be more lean upon acceleration, the fuel control system is adapted to inject fuel in an increased fuel amount during acceleration, so as to prevent the fuel mixture from becoming lean. Such an intake system is known from Japanese Patent Publication No. 49(1974)-45655, entitled "Injection Type Fuel Distribution Apparatus," published Dec. 5, 1974.
Such a fuel control system as that described in the above publication generally judges the acceleration of automobile by detecting, for example, an increase of intake air greater than a standard increase. In this fuel control system, because fuel is apt to be difficult to gasify or vaporize before the engine warms up and, accordingly, has an increased viscosity, the fuel mixture becomes lean immediately after the start of automobile when an increase of intake air is smaller than the standard increase level or upon quick and slight acceleration. In such cases, the fuel control system can not judge wheter the automobile is subjected to acceleration, resulting in not injecting fuel with an increase in fuel amount and in failing to prevent the fuel mixture from becoming lean.